This invention relates to apparatus for forming a reliable metal joint and, in particular, to apparatus for soldering aluminum connections to aluminum heat exchanger tubes so as to establish a highly reliable bond there between.
In condensers and evaporators as typically employed in the air conditioning art, the joints between the tubular components of the heat exchanger must provide a reliable high strength seal to assure the fluid tight integrity of the unit. The forming of these joints, particularly where the tubular components are made of aluminum, presents a number of problems. Some of these problems are overcome by the ultrasonic dip soldering process wherein the joints are submerged within a bath of molten solder and the bath then treated with ultrasonic energy. The ultrasonic energy functions to remove oxide coatings from the aluminum components and thus permit solder to wet the metal surfaces whereby a good metallurgical bond is formed.
The untrasonic dip process has achieved a certain degree of success, however, it has been found that the heat exchanger structure which is specifically designed as a highly efficient heat transfer device, has the ability to drawn an inordinate amount of heat out of the joint region during the soldering process. To overcome this unwanted drain of energy, the heat exchanger structure is normally preheated to a temperature slightly above the soldering temperature prior to the joints being immersed in the molten bath. The preheated unit, however, must be handled and transported some distance prior to the joints being submerged in the bath. As a result, it is extremely difficult to maintain the exchanger structure at a constant predetermined temperature level.